Fluid-pressure transducer

ABSTRACT

Apparatus for converting a change in fluid-pressure into mechanical motion of a part, which motion can be used to generate a suitable output signal. Two bands affixed to a sheave are wound thereon, side by side, in opposite directions. The free ends of the bands are connected to a pushrod which is in the same plane and at right angle to the axis of the sheave. The clockwise wound band is connected to the right of the axis of the sheave and other band is connected to the left thereof. The pushrod is connected at one of its ends to a pressure capsule which deflects when the fluid-pressure acting thereon is changed. This deflection causes the sheave to rotate and generate the desired output effect.

United States Patent Segerdahl et al.

[451 July 11,1972

[54] FLUID-PRESSURE TRANSDUCER [72] Inventors: Roy R. Segerdahl,Belmore; Joseph L.

21 Appl. No.: 781,333

3,173,120 3/1965 Marks et a1. ..338/41 X Primary Examiner-Rodney D.Bennett, Jr.

Assistant Examiner-Brian I... Ribando Attorney-Frederick M. Arbuckle[57] ABSTRACT Apparatus for converting a change in fluid-pressure intomechanical motion of a part, which motion can be used to generate asuitable output signal. 'l'wo bands affixed to a 52 C| 41 sheave arewound thereon, side by side, in opposite directions. In CL mnolc 11400The free ends of the bands are connected to a pushrod which [58] Fieldof Search ..338/41 42 is the same Plane and angle The clockwise woundband is connected to the right of the 56 v axis of the sheave and otherband is connected to the left 1 References Cited thereof. The pushrod isconnected at one of its ends to a pres- UNITED STATES PATENTS surecapsule which deflects when the fluid-pressure acting thereon ischanged. This deflection causes the sheave to rotate 3 2 2; i at andgenerate the desired output effect. ramer.... 3,136,969 6/1964 Mollick..338/41 3 Claim, 2 Drawing Figures '10 3 I00 240- 5| WTE 2 PatentedJuly 11, 1972 3,676,821

ROY RSEGERDAHL JOSEPH L. JONKE -1 NVENTORS FLUID-PRESSURE TRANSDUCERBACKGROUNDOF THE INVENTION This invention relates to fluid-pressuretransducers and while it is of general application in accuratelyconverting linear to rotary motion, it is particularly suitable forembodiment in such a transducer for adjusting the contact of anelectrical potentiometer and will be described in such an embodiment.

Heretofore, there have been devised many fluid-pressure transducers foroperating control devices such as potentiometers. However, these priortransducers have had several disadvantages when used to respond torelatively low pressures, especially when utilized in an applicationwhich subjects them to large acceleration and vibration forces, such asin missiles and aircraft for the measurement of barometric pressure. Forexample, they have customarily comprised a pressure capsule or diaphragmof fairly rugged construction to withstand acceleration forces and, whenmeasuring the relatively low pressures, the amount of deflection hasbeen necessarily limited requiring the addition of motion multiplyingmechanisms which are relatively complex and costly. These mechanisms, bytheir very nature, introduce errors when they are subject toenvironmental accelerations and vibrations.

It is an object of this invention, therefore, to provide a new andimproved fluid-pressure transducer which obviates one or more of theabove mentioned disadvantages of the prior art devices.

It is another object of the invention to provide a new and improvedfluid-pressure transducer capable of operating satisfactorily atrelatively low pressures while substantially eliminating errors due tofriction of the moving parts and to the effects of vibration andaccelerating forces.

It is a further object of the invention to provide an inexpensivefluid-pressure transducer of the type described.

SUMMARY OF THE INVENTION In accordance with the invention there isprovided a fluidpressure transducer comprising a support; a pressuredeflectable element disposed to deflect in response to a change influid-pressure; a pushrod directly and positively secured to thedeflectable element; a sheave located substantially in the same plane asthe pushrod and rotatably mounted on the support having its axis ofrotation substantially perpendicular to the pushrod; a pair of bands,each affixed to one end of the sheave and wound thereon, side by side,in opposite directions, the free end of the clockwise wound band beingconnected to the pushrod at a point to the right of the axis of thesheave, and the free end of the counterclockwise wound band beingconnected to the pushrod at a point to the left of the axis of thesheave; and means actuated by the pushrod for utilizing the displacementof the deflectable element to develop an output effect.

For a better understanding of the present invention together withfurther objects and features thereof, reference is had to the followingdescription, to be read in conjunction with the accompanying drawings,wherein like components in the several views are identified by the samereference numeral, while its scope will be pointed out in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview of a fluid-pressure transducer embodying the invention.

FIG. 2 is cross sectional view taken along the lines 22 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more specifically tothe drawings, there is illustrated a fluid-pressure transducer embodyingthe invention comprising a support and a fluid-pressure inlet. Thesupport may be in the form of a supporting member to which the remainingelements of the transducer are affixed directly or indirectly. The sizeof fluid-pressure inlet 11 is detennined by the size of the opening ininlet housing 12. It should be noted that inlet housing 12 may bedispensed with, in which case, inlet 11 would comprise the entire areaenclosed by housing 12.

The transducer of the invention further comprises a pressure-deflectableelement, such as pressure capsule 13, which is accessible to inlet 11.There must be a pressure tight seal between the junction point ofcapsule l3 and support 10. This may be accomplished by any conventionalmeans, such as soldering. Capsule 13 is disposed to deflect upon achange in the fluid pressure applied to inlet 11.

The transducer further comprises a pushrod 14 directly and positivelysecured to capsule l3. Pushrod 14, which passes through hole 10a insupport 10, may be secured to capsule 13 by threading the end of pushrod13 and employing a nut 15 as a fastener. In this regard it should benoted that the junction between capsule 13 and pushrod 14 must be sealedso as to be capable of withstanding applied pressures without leaking.This may be accomplished in any suitable manner, for example, a bushing16 may be soldered to capsule l3 and urged against the lip of flange 17by tightening nut 15 thereby effecting the required seal. It may also benecessary to solder or otherwise seal the junctions between nut 15,bushing 16, flange l7 and the screw threads of pushrod 14 to effect aproper seal. The free end of pushrod 14 may be supported by anantifriction bushing such as Teflon bushing 18.

The transducer still further includes a sheave 19 which is substantiallyin the same plane as pushrod l4. Sheave 19 is rotatably mounted on shaft20 which may inturn be mounted on bearings 21 and 22 held by support 10.The axis of rotation of sheave 19 is substantially perpendicular topushrod 14.

It is hereby defined, for purposes of this description, as well as theappended claims that an increase in inlet pressure causes a deflectionof pushrod 14 to the right and a decrease in inlet pressure causes adeflection of pushrod 14 to the left. This relationship is to beunderstood even if in actuality the transducer is viewed in a specificorientation which would normally require the opposite relationship toexist. Therefore, for right and left as used in the specification andclaims to correspond to reality, the transducer, illustrated in FIG. 1,should be viewed with inlet 11 to the viewers left.

The transducer further comprises a pair of bands 23 and 24, each ofwhich is affixed at one end to sheave 19 at points 230 and 24arespectively. Bands 23 and 24 wind on sheave 19, side by side, inopposite directions. The other ends of bands 23 and 24 are connected topushrod 14 at points 23b and 24b respectively. A deflection of pushrod14 to the right will cause band 23 to wind on to sheave I9 and band 24to unwind from sheave 19. Conversely, a deflection of pushrod 14 to theleft will cause band 24 to wind on to sheave 19 and band 23 to unwindfrom sheave 19. Therefore, it is readily seen that the minimum length ofeither band that must be wound on sheave 19 is dependent upon themaximum deflection of pushrod 14.

For a reason analogous to that outlined above, the distance betweenpoints 23b and 24b and a vertical line passing through the axis ofrotation of sheave 19 is also dependent upon the maximum deflection ofpushrod 14. This is due to the fact that the bands must be free to windand unwind on sheave 19, as described, without restrictions for the fullrange of pushrod l4 deflections in both directions. The connections atpoints 23a, 23b, 24a, and 24b may be made in any conventional manner,for example, by welding.

In order to make the transducer unresponsive to acceleration forces acounterweight 25 may be employed. Counterweight 25 is secured to bracket26 which in turn is secured to sheave 19 by any conventional means suchas welding.

The fluid-pressure transducer of the invention further comprises meansfor utilizing the rotation of sheave 19 caused by the displacement ofcapsule 13 to develop an output effect. This means preferably is in theform of an elongated electrical impedance or resistance element 27supported on bracket 28 and having insulated terminals 29 and 29a.Resistance element 27 is secured to bracket 28 in any conventionalmanner, for example, adhesive. An elongated and insulated wiper element30, is afiixed to terminal 31 at point 31a by riveting or other suitablefastening means. Terminal 31 is supported by bracket 26 which, as waspreviously explained, is also used to support counterweight 25. Upon adeflection of capsule 13, the relative displacement between wiperelement 30 and resistance element 27 is greater than the deflection ofpushrod 14. This multiplication of capsule deflection increases theaccuracy of the output signal, especially for low pressure readings. Thewires (not shown) which are connected to terminals 29a, 29b, and 31 maybe connected to the terminals of connector 32.

It should also be noted that the above described mechanism converts thelinear deflection of pushrod 14 into an angular motion of wiper 30. Thisangular wiping motion results in a continued change of wiper contactpoint between wiper 30 and resistance element 27 as pushrod 14 isdeflected. This minimizes electrical noise as it assures a cleanconnection between wiper 30 and resistance element 27.

The pressure transducer described may be encased in an enclosed housing33 hermetically sealed to support 10. If the transducer is to respond toabsolute pressure then either housing 33 must be evacuated or the outputsignals must be biased to compensate for atmospheric pressure. If it isdesired to respond to differential fluid pressure, a fluid connection(not shown) may be made to housing 33 so that the two fluid pressuresmay be applied to inlet 11 and housing 33, respectively.

It is believed that the operation of the transducer of the presentinvention will be clear from the foregoing description. Briefly, it maybe assumed that the transducer is to respond to an absolute fluidpressure applied to inlet 11. If the absolute pressure increases,capsule 13 will be compressed and displace pushrod 14 to the right. Thisdisplacement will, by means of bands 23 and 24, cause sheave 19 torotate. When sheave 19 rotates it causes relative displacement betweenresistance element 27 and wiper element 30 which change may be indicatedby a signal appearing at connector 32. This relative displacementbetween resistance element 27 and wiper element 30 is greater than thedisplacement of pushrod 14. This motion multiplication is accomplishedwithout any motion multiplying mechanism.

Obviously, if the absolute pressure applied to inlet 11 decreases,similar action takes place but in an opposite direction. It is alsoobvious that, if desired, the transducer may respond to a differentialpressure rather than to an absolute pressure. As described above, thetransducer responds to the difference between the two fluid pressuresapplied to inlet 11 and housing 33 respectively. The operation of thetransducer per se is the same whether it responds to absolute ordifferential pressure.

The transducer, as described, is substantially unresponsive toacceleration and vibration forces in any direction. Such a force havinga component along the axis of pushrod 14 would, of course, deflectcapsule 11 unless it were compensated for by another opposing force.However, in the present invention the axial component of the inertiaforce of the transducer, including the force due to the mass ofcounterweight 25, serves to oppose the deflection of capsule 13 causedby any force of acceleration or vibration. Therefore, if the mass ofcounterweight 25 is properly selected, it will balance any accelerationor vibration forces acting to cause relative motion between resistanceelement 27 and wiper element 30 thereby reducing or eliminating anyerror which would otherwise result.

Now the benefit of utilizing opposing bands 23 and 24 can be seen. If asingle band were employed, it would be able to compensate for theacceleration forces acting on capsule 13 only in one axial direction.Here, one or the other of bands 23 or 24 will effectively couple themass of counterweight 25 to the unbalanced transducer mass, regardlessof the axial direction of the acceleration or vibration force, to effecta cancellation of any unbalance force. In addition, any lost motion canbe eliminated by pretensioning bands 23 and 24 during welding. With thistype of arrangement, testing has shown that the present invention isrelatively insensitive to vibration over broad magnitude and frequencyspectrums.

Thus, it is seen that the fluid-pressure transducer described has anumber of advantageous characteristics not found in prior devices ofthis type:

1. A direct and positive drive of wiper element 30 without theinterposition of any costly motion-multiplying mechanism which wouldcause errors by introducing friction into the device.

2. Substantial elimination of the effect of acceleration and vibrationforces, any such force being effectively cancelled out by opposing forcecoupled by means of the bands 23 and 3. Angular wiping betweenresistance element 27 and wiper element 30, minimizing electrical noiseand multiplying the relative motion therebetween.

While what has been shown and described is believed to be the best modeand preferred embodiment of the invention, modifications and variationscan be made therein, as will be clear to those skilled in the art,without departing from the spirit of the invention and consequently, thescope of the invention is intended to bev limited solely by the appendedclaims.

What is claimed is:

l. A fluid-pressure transducer comprising:

a support;

a pressure-deflectable element disposed to deflect in response to achange in fluid pressure;

a pushrod directly and positively secured to said deflectable element;

a sheave located substantially in the same plane as said pushrod androtatably mounted on said support having its axis of rotationsubstantially perpendicular to said pushrod;

means for connecting said pushrod to said sheave in a manner such thatany linear movement of said pushrod in response to the deflection ofsaid deflectable element results in a pulling force being exerted onsaid sheave to cause a corresponding rotation thereof, there being nolost motion between said pushrod and sheave introduced by saidconnecting means; and

means actuated by the rotation of said sheave in response to thedeflection of said deflectable element for developing an output effect.

2. A fluid-pressure transducer comprising:

a support;

a pressure-deflectable element disposed to deflect in response to achange in fluid pressure;

a pushrod directly and positively secured to said deflectable element;

means for slideably mounting the free end of said pushrod;

a sheave located substantially in the same plane as said pushrod androtatably mounted on said support having its axis of rotationsubstantially perpendicular to said pushrod;

a pair of flexible bands, each of which is affixed at one end to saidsheave and wound thereon side by side in opposite directions;

the free end of the first of said pair of bands being connected to saidpushrod at a point on one side of the axis of said sheave; and

the free end of the second of said pair of bands being connected to saidpushrod at a point on the opposite side of the axis of said sheave;

said bands being pretensioned to eliminate lost motion between saidsheave and said pushrod;

means actuated by the rotation of said sheave in response to thedeflection of said deflectable element for developing an output effect;and

a counterweight attached to said sheave;

whereby, since there is no lost motion between said sheave and saidpushrod, the effect of vibration and acceleration forces on said outputdeveloping means may be completesaid sheave and the other end of whichis in electrical ly balanced and eliminated by said counterweight.contact with said impedance element; I

Pf 'b accorqancef i clalmf 2 whereby any displacement of saiddeflectable element g z "Si iiggzi i g f gg Sad sheave or 5 causes saidcontact element to change its contact position eve Op Pu p on saidimpedance element.

an electrical impedance element; and an insulated contact element oneend of which is affixed to

1. A fluid-pressure transducer comprising: a support; apressure-deflectable element disposed to deflect in response to a changein fluid pressure; a pushrod directly and positively secured to saiddeflectable element; a sheave located substantially in the same plane assaid pushrod and rotatably mounted on said support having its axis ofrotation substantially perpendicular to said pushrod; means forconnecting said pushrod to said sheave in a manner such that any linearmovement of said pushrod in response to the deflection of saiddeflectable element results in a pulling force being exerted on saidsheave to cause a corresponding rotation thereof, there being no lostmotion between said pushrod and sheave introduced by said connectingmeans; and means actuated by the rotation of said sheave in response tothe deflection of said deflectable element for developing an outputeffect.
 2. A fluid-pressure transducer cOmprising: a support; apressure-deflectable element disposed to deflect in response to a changein fluid pressure; a pushrod directly and positively secured to saiddeflectable element; means for slideably mounting the free end of saidpushrod; a sheave located substantially in the same plane as saidpushrod and rotatably mounted on said support having its axis ofrotation substantially perpendicular to said pushrod; a pair of flexiblebands, each of which is affixed at one end to said sheave and woundthereon side by side in opposite directions; the free end of the firstof said pair of bands being connected to said pushrod at a point on oneside of the axis of said sheave; and the free end of the second of saidpair of bands being connected to said pushrod at a point on the oppositeside of the axis of said sheave; said bands being pretensioned toeliminate lost motion between said sheave and said pushrod; meansactuated by the rotation of said sheave in response to the deflection ofsaid deflectable element for developing an output effect; and acounterweight attached to said sheave; whereby since there is no lostmotion between said sheave and said pushrod, the effect of vibration andacceleration forces on said output developing means may be completelybalanced and eliminated by said counterweight.
 3. A pressure transducerin accordance with claim 2 wherein said means actuated by the rotationof said sheave for developing an output effect comprises; an electricalimpedance element; and an insulated contact element one end of which isaffixed to said sheave and the other end of which is in electricalcontact with said impedance element; whereby any displacement of saiddeflectable element causes said contact element to change its contactposition on said impedance element.